Typically, piston rods tend to wear along that portion of the rod which extends (reciprocates) through the rod opening in the end caps of a fluid actuator. Such wear is the result of frictional engagement between the rod surface and the peripheral surface of the rod opening in the end cap and generally results in leakage of actuator fluid around the worn surface. To stop the leakage, the system in which the actuator is used is shut down, and the actuator is removed so that the entire piston and piston rod assembly can be replaced; however, some typical fluid actuators are very heavy and difficult to handle during installation in a fluid system or removal from a fluid system because of the extreme bulk. The body of the actuators are generally made of heavy cast metal, and adding to this weight is the weight of the piston and piston rod assembly. In some instances, a piston rod of 20 feet or more may be required. It is necessary that the piston rod have a very hard outer surface along the portion which reciprocates through the opening of the end cap of the actuator assembly to prevent excessive wear to the surface of the piston rod. The entire rod is typically made of a single durable material so that excessive wear does not affect the durability of the rod. However, such material is very heavy and adds to the weight problem as discussed above.
The present invention overcomes such noted difficulties by providing a rod having a tough durable outer shell member along the portion which reciprocates through the end caps of the fluid actuator assembly. Preferably, the rod body is made of lighter weight material by volume (per cubic inch) than the outer shell material, i.e., the density of the rod is less than that of the outer shell, and the outer shell member is made removable and is made of a hardened material to prevent excessive wear thereto as a result of its reciprocal movement through the end cap of the actuator. If the outer surface becomes pitted or worn, only the outer casing need be replaced, thus eliminating the need to replace the entire piston rod.